When I remove the battery, I can attach a USB charger to the D4, select switch to USB, and I can listen to my DAP through Line in with my headphones plugged in to the Headphone out.   Hope I'm not damaging anything...

I also find the Sure's to have a good deal of bass with a flat EQ and more than enough with the smallest boost.

These phones sound quite good for the price.  They are driven surprisingly easily unamped, and only sound marginally better with an amp.   I have been driving them with my ibasso d4 through my pc and can barely tolerate anything else now.  When I run it through my rockboxed clip, can't seem...